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SP6659 Datasheet(PDF) 6 Page - Sipex Corporation |
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SP6659 Datasheet(HTML) 6 Page - Sipex Corporation |
6 / 10 page 6 Date: 07/20/05 SP6659 1.5MHz, 600mA Synchronous Buck Regulator © Copyright 2005 Sipex Corporation APPLICATION INFORMATION A resistive divider based on the following equation determines the output voltage: VOUT = 0.6 (1+ ) The external resistive divider is connected to the output as shown in Figure 7 . ® SP6659 GND R1 R2 VFB VOUT Figure 7: Setting the SP6659 Output Voltage. R2 R1 The SP6659 is a monolithic switching mode Step-Down DC-DC converter. It utilizes in- ternal MOSFETs to achieve high efficiency and can generate very low output voltage by using its internal reference at 0.6V. It operates at a fixed switching frequency, and uses slope compensated, current-mode architecture. This Step-Down DC-DC con- verter supplies 600mA of output current at VIN = 3V. The entire input voltage range is from 2.5V to 5.5V. __________________ CURRENT MODE PWM CONTROL Slope compensated current mode PWM control provides stable switching and cycle- by-cycle current limit for excellent load and line responses and protection of the internal main switch (P-Channel MOSFET) as well as the synchronous rectifier (N-Channel MOSFET). During normal operation, the in- ternal P-Channel MOSFET is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current is above the error voltage. The THEORY OF OPERATION current comparator, ICOMP, limits the peak inductor current. When the main switch is off, the synchronous rectifier will be turned on immediately and stay on until either the inductor current starts to reverse, as indi- cated by the current reversal comparator, IZERO, or the beginning of the next clock cycle. The OVDET comparator controls output transient overshoots by turning the main switch off and keeping it off until the fault is no longer present. _______________________ IDLE MODE OPERATION At very light loads, the SP6659 automati- cally enters Idle Mode (Figure 8). In the Idle Mode, the inductor current may reach zero Amps or reverse on each pulse. The PWM control loop will automatically skip pulses to maintain output regulation. The bottom MOSFET is turned off by the current rever- sal comparator, IZERO, and the switch volt- age will ring. This is discontinuous mode operation, and is normal behavior for the switching regulator. |
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